Reduced weight golf club shafts

ABSTRACT

Improved methods for manufacturing a shaft for a golf club, devices useful in such methods, and golf club shafts manufactured in accordance with such methods. A plug is detachably affixed to a distal end of a mandrel. A plurality of plies of pre-preg composite sheet are wrapped around the mandrel and plug and, thereafter, heated causing the resin comprising the various plies to be cured. The mandrel is then removed from the formed shaft, leaving the plug as an integral part of the distal tip of the shaft.

BACKGROUND OF THE INVENTION

The field of the present invention is golf club shafts and, more particularly, reduced weight golf club shafts and methods of manufacturing the same.

Recently, substantial attention has been directed toward the development of lightweight golf club shafts which are manufactured from various composite materials or, more particularly, from a set of plies of "pre-preg" composite sheet. Pre-preg composite sheets are formed by pre-impregnating strands of fiber, for example, carbon or glass, within a binding matrix such as a thermoset epoxy resin or thermoplastic resin. The binding matrix or resin is staged such that it holds the fibers together and forms a malleable sheet.

Numerous shafts are now manufactured by wrapping a set of plies of pre-preg composite sheet around a mandrel in a predetermined manner, wrapping the various plies in a binding material such as cellophane or polypropylene tape, and heating the ply-wrapped mandrel to a predetermined temperature for a time sufficient to allow the resin comprising the plies of pre-preg composite sheet to become fully cured. Once the resin has been fully cured, the binding material may be removed from the exterior of the shaft, and the mandrel may be removed from the core of the shaft. Finally, the shaft may be lightly sanded and painted prior to being inserted into a golf club head.

Through the use of composite materials, it has become possible to manufacture reduced weight shafts for golf clubs, and many shaft manufacturers are now offering for sale ultralight shafts having, for example, a mass less than 70 grams. The extent to which the weight of a shaft may be reduced, however, is limited substantially by the structural requirements that must be met by the tip of the shaft that is affixed within the golf club head. In short, if the walls of the shaft tip are made too thin in an effort to reduce the weight of the shaft, the tip will likely fail or shatter during use. This is particularly true for those golf club head designs that employ a shortened hosel, as such designs provide less structural support for the shaft tip.

It will also be noted that, when a golf club head incorporates a bored-through design whereby the shaft extends through the club head, it is generally necessary to affix a plug in the open end of the shaft tip after the shaft tip has been inserted through the golf club head. This gives the assembled golf club a pleasing cosmetic appearance and, more importantly, prevents debris from entering the shaft tip. However, the use of conventional plugs provides little, if any, structural support to the shaft tip.

Finally, it will be noted that many conventional shaft tips are damaged during trimming processes. Once a shaft is formed, it is common to trim the shaft by removing a segment from both the butt end of the shaft and the tip end. If the walls of the tip are too thin, or if proper care is not taken during the trimming process, serious damage may be caused to the tip during the trimming process.

In view of the many problems that may be encountered in designing and manufacturing reduced weight shafts for golf clubs, it is submitted that those skilled in the art would find improved golf club shafts with reinforced tips and methods of manufacturing such shafts to be quite useful.

SUMMARY OF THE INVENTION

The present invention is directed toward improved methods of manufacturing shafts for golf clubs and to golf club shafts manufactured in accordance with those methods.

In one innovative aspect, the present invention is directed toward a method of manufacturing a shaft for a golf club wherein a plug reinforces and forms an integral portion of a shaft tip. In one such embodiment, a plug is adapted to mate with a distal tip portion of a mandrel. Plies of pre-preg composite sheet may then be wrapped around a portion of the plug and mandrel in a predetermined manner, the plies of pre-preg composite sheet may be wrapped in a binding material such as cellophane or polypropylene tape, and the ply-wrapped mandrel may be heated for a time sufficient to allow the resin in the plies of pre-preg to fully cure. Thereafter, the binding material may be removed from the exterior of the shaft, and the mandrel may be removed from the core of the shaft. The shaft and integral plug may then be trimmed, inserted into a golf club head and affixed within the club head using an epoxy resin. Further, where bored-through head designs are employed, the portion of the plug and shaft tip that extends out from the sole of the club head may be cut off and properly sanded to be flush with the sole. In such instances, a substantial portion of the integral plug preferably will remain within the shaft tip after the protruding portion of the shaft tip has been cut and sanded, thus providing substantial structural support to the shaft tip. The use of an integral plug in accordance with the present invention also facilitates the design and manufacture of reduced weight golf club shafts.

In other innovative aspects, the plug may be formed from a thermally expandable material, and the shaft and integral plug may be manufactured via the cellowrap method described above or via a molding process. In one such embodiment, a bladder may be provided over a mandrel before the plug is fitted onto a male extension provided at a distal tip of the mandrel. Plies of pre-preg composite sheet may then be wrapped around the bladder covered mandrel and plug in a predetermined manner, and the ply wrapped mandrel and plug may be placed in a mold. If desired, the mandrel may then be withdrawn from the mold leaving the bladder, plug and surrounding plies of pre-preg within the mold. Alternatively, the ply-wrapped mandrel may be left in the mold. In either case, the bladder may be inflated to a predetermined pressure to force the plys of pre-preg against the walls of the mold, and the mold may be heated to a predetermined temperature for a time sufficient to allow the resin comprising the plies of pre-preg to fully cure. Thereafter, the shaft and integral plug may be removed from the mold, the mandrel (if not previously removed) may be removed from the core of the shaft, and the bladder may be removed from the core of the shaft. It will be noted that in such an embodiment, the thermally expansive material comprising the plug will provide not only increased compaction of the plies of pre-preg in the tip region during the curing process, but also substantial structural support in the shaft tip after the curing process has been completed.

In still another innovative aspect, a plug in accordance with the present invention may have one or more hoop ring indentations formed in its exterior surface. In such an embodiment, a shaft may be manufactured in the various manners set forth above. However, during the curing process, resin may be forced into the hoop ring recesses of the plug to more securely affix the plug within the shaft tip.

In still another innovative aspect, the present invention is directed to a mandrel and plug for use in manufacturing a shaft for a golf club. In a preferred form, the mandrel has a distal tip that is notched to form a male extension, and the plug is adapted to detachably receive the male extension.

Accordingly, it is an object of the present invention to provide improved methods for manufacturing golf club shafts.

It is also an object of the present invention to provide improved golf club shafts and, in particular, reduced weight golf club shafts that are manufactured in accordance with such methods.

It is still another object of the present invention to provide innovative mandrel and plug combinations for use in the manufacture of golf club shafts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a conventional linearly tapered mandrel.

FIG. 2 is an illustration of a mandrel with a male extension and pre-molded plug in accordance with one embodiment of the present invention.

FIG. 3(a) illustrate a pre-molded plug having exterior walls that taper toward the distal tip of the plug.

FIG. 3(b) illustrates a pre-molded plug having parallel walls.

FIG. 3(c) illustrates a pre-molded plug having reverse tapered walls.

FIG. 4 is a cross-sectional illustration of a plurality of plies of pre-preg wrapped around a mandrel and plug combination in accordance with the present invention.

FIG. 5 is a cross-sectional illustration of a shaft tip and plug in accordance with the present invention.

FIG. 6 illustrates the removal of a mandrel from a shaft and integral plug in accordance with the present invention.

FIG. 6(a) illustrates the removal of a mandrel from a shaft and intergral plug having a reverse-taper in accordance with the present invention.

FIG. 7 is an illustration of a shaft inserted through a bored-through golf club head with a portion of the shaft and integral plug extending out from the sole of the club head.

FIG. 8 is a cross-sectional illustration of a shaft tip and integral plug after a trimming operation.

DESCRIPTION OF PREFERRED EMBODIMENTS

Turning now to the drawings, FIG. 1 provides an illustration of a conventional mandrel 10 that may be used during the manufacture of conventional composite golf club shafts. Such shafts may be manufactured, for example, by wrapping plies of pre-preg carbon fiber sheet around the mandrel 10 in a predetermined manner, wrapping the plies in a binding material such as cellophane or poylpropylene tape, and heating the wrapped mandrel 10 to a predetermined temperature for a time sufficient to allow the resin comprising the various plies to be fully cured.

As shown in FIG. 2, a mandrel 12 in accordance with one form of the present invention is generally similar in shape to the mandrel 10 shown in FIG. 1, except that the distal tip 14 of the mandrel 12 is notched to form a male extension 16. The male extension 16 is designed to fit within a central cavity 18 formed in a pre-molded plug 20. In a presently preferred form, the pre-molded plug 20 may be substantially 5 inches in length and may comprise a material that exhibits substantial thermal expansion such as thermally expansive foam, rubber or silicone. Further, it will be noted that once the plug 20 is fitted on the male extension 16 of the mandrel 12, the mandrel 12 and plug 20 combination illustrated in FIG. 2 may have substantially the same dimensions as the mandrel 10 illustrated in FIG. 1. Thus, the mandrel 12 and plug 20 combination may be used to manufacture golf club shafts in all of the ways that the mandrel 10 illustrated in FIG. 1 may be used. It will be understood that in alternative embodiments a mandrel may be shaped to accept a plug without being notched. In addition, the plug may take several forms. For example, as shown in FIGS. 3(a)-(c), the exterior walls 21 of the plug 20 may be tapered toward the distal tip 23 of the plug 20, the walls 21 of the plug 20 may be configured in a parallel fashion, or the walls 21 of the plug 20 may exhibit a reverse taper.

As shown in FIG. 4, a plurality of plies 22 of pre-preg composite sheet may be wrapped around or "layed-up" on the mandrel 12 and plug 20 combination in a predetermined manner, the plies 22 of pre-preg may be wrapped in a heat shrinkable, binding material such as cellophane tape (not shown), and the wrapped mandrel 12 and plug 20 combination may be heated to a predetermined temperature for a time sufficient to allow the resin comprising the plies of pre-preg to fully cure. Thereafter, the mandrel 12 may be removed from the core 24 of the shaft 26 (as shown in FIG. 6) leaving the plug 20 as an integral portion of the shaft 26. Any portion of the plug 20 that is not fixed within the shaft tip 28 may also be cut away (as shown in FIG. 8). In a preferred form, the plies 22 of pre-preg may comprise pre-preg carbon fiber sheet, and the plies 22 of pre-preg may cover a 1-4 inch section of the plug 20. However, those skilled in the art will recognize that numerous composite materials may be substituted for the carbon fiber, and that longer or shorter plugs may be employed depending upon the overall design of a given shaft.

In another preferred embodiment, the shaft 26 and integral plug 20 may be manufactured via a molding process. In such an embodiment, a bladder (not shown), formed, for example, from latex, rubber or silicone, may be provided over the mandrel 12 before the plug 20 is fitted onto the male extension 16 provided at a distal tip of the mandrel 12. Plies 22 of pre-preg composite sheet may then be wrapped around the bladder covered mandrel 12 and plug 20 in a predetermined manner, and the ply wrapped mandrel 12 and plug 20 may be placed in a mold (not shown). If desired, the mandrel may then be withdrawn from the mold leaving the bladder (not shown), plug 20 and surrounding plies 22 of pre-preg carbon fiber within the mold. Alternatively, the ply-wrapped mandrel 12 and plug 20 combination may be left assembled in the mold. In either case, the bladder (not shown) may be inflated to a predetermined pressure (for example, from 100 to 300 psi) to force the plys 22 of pre-preg against the walls of the mold, and the mold may be heated to a predetermined temperature (for example, to between 250° and 800° F. depending upon the resin used) for a time sufficient to allow the resin comprising the plies 22 of pre-preg to fully cure. Thereafter, the shaft 26 and integral plug 20 may be removed from the mold, the mandrel 12 (if not previously removed) may be removed from the core 24 of the cured shaft 26, and the bladder (not shown) may be removed from the core 24 of the shaft 26..

Finally, it will be appreciated that the shaft 26 and integral plug 20 may be manufactured via a filament winding process or via a combination of filament winding and prepreg wrapping processes. As filament winding techniques are well known in the art, those techniques are not discussed in detail herein. Rather, it is sufficient to understand that filament winding techniques together with resin injection in a molding process may be used to form a shaft 26 and integral plug 20 in accordance with the present invention.

It will be noted that, where the plug 20 is formed from a thermally expansive material, the thermally expansive material comprising the plug 20 will provide increased pressure in the shaft tip 28 during the curing process. This results in tighter compaction of the plies 22 of pre-preg in the shaft tip 28 and reduces the risk that structural defects may develop in the tip region during the curing process. The plug 20 also will provide substantial structural support in the shaft tip 28 after the curing process has been completed.

Turning back to FIGS. 2 and 4, a plug 20 in accordance with the present invention may have one or more hoop ring indentations 30 formed in its exterior surface. In such an embodiment, a shaft 26 may be manufactured in the manner set forth above. However, during the curing process, resin may be forced into the hoop ring recesses 30 of the plug 20 to more securely affix the plug 20 within the shaft tip 28.

As shown in FIG. 7, a shaft tip 28 and integral plug 20 in accordance with the present invention may be inserted into and through a bored-through golf club head 36 such that a distal portion 38 of the shaft 26 and integral plug 20 extends out from the sole 39 of the club head 36. After the shaft 26 is affixed in the club head 36, for example, by bonding with an epoxy resin, the distal portion 38 of the shaft 26 and plug 20 may be cut off and sanded flush with the sole 39 of the club head 36. Of course, in a preferred form, a substantial portion, for example, a 2 to 4 inch section, of the integral plug 20 will remain within the shaft tip 28 after the distal portion 38 of the shaft 26 and plug 20 has been removed or trimmed from the shaft tip 28. This is shown, for example, in FIG. 8.

While the invention is susceptible to various modifications and alternative forms, specific examples thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms or methods disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims. 

What is claimed is:
 1. A shaft for a golf club, said shaft comprisinga shaft body with a proximal end, a distal end, and an integral plug, said shaft body having a generally frusto-conical shape, being tapered in a first direction at said distal end, and having a cavity extending along its longitudinal axis from said proximal end to said distal end, and said integral plug having a profile that exhibits a taper in a direction opposite the direction of taper of said shaft body at said distal end and being affixed within said distal end of said shaft body.
 2. The shaft of claim 1, wherein said plug comprises a thermally expansive material.
 3. A shaft for a golf club, said shaft comprisinga shaft body and an integral plug, said shaft body having a generally cylindrical shape that tapers in a first direction and having a cavity formed in and extending along a longitudinal axis thereof, said integral plug being affixed within a distal end of said shaft body and having a proximal end wherein a cavity for detachably receiving a mandrel tip is provided.
 4. The shaft of claim 3, wherein said integral plug has a taper in a direction opposite to said first direction.
 5. The shaft of claim 3, wherein said integral plug has a taper in a direction common to said first direction.
 6. The shaft of claim 3, wherein said integral plug is formed from a thermally expansive material.
 7. A shaft for a golf club, said shaft comprisinga shaft body and an integral plug, said shaft body having a generally cylindrical shape that tapers in a first direction and having a cavity formed in and extending along a longitudinal axis thereof, said integral plug comprising a thermally expansive material, being affixed within a distal end of said shaft body and having a proximal end wherein a cavity for detachably receiving a mandrel tip is provided.
 8. A shaft for a golf club, said shaft comprising:a body comprising a plurality of composite fibers fixed within a binding matrix, said body having a generally cylindrical shape that tapers in a first direction and having a central cavity extending along a longitudinal axis thereof, and an integral plug, said integral plug being co-cured within a distal region of said central cavity of said body such that a portion of said binding matrix adheres to and fixes a position of said integral plug within said distal region of said central cavity, wherein said integral plug has a proximal end wherein a cavity for detachably receiving a mandrel tip is provided. 